Field of the Invention
The present invention relates to an automatic transmission for a vehicle. More particularly, the present invention relates to a planetary gear train of an automatic transmission for a vehicle that improves power delivery performance and reduces fuel consumption by achieving eleven forward speed stages and widening gear ratio span using a minimum number of constituent elements.
Description of Related Art
In recent years, a rise in oil price caused unlimited competition for enhancing fuel efficiency.
As a result, research is being conducted on engines in terms of reducing weight and improving fuel efficiency by down-sizing, and research is also being conducted for simultaneously securing operability and fuel efficiency competitiveness by implementing an automatic transmission with multiple speed stages.
However, in the automatic transmission, as the number of speed stages increase, the number of internal components increase, and as a result, the automatic transmission may be difficult to mount, the manufacturing cost and weight may be increased, and power transmission efficiency may be deteriorated.
Accordingly, development of a planetary gear train which may bring about maximum efficiency with a small number of components is important in order to increase a fuel efficiency enhancement effect through the multiple speed stages.
However, since a conventional 8-speed automatic transmission has gear ratio span of 6.5-7.5, improvement of fuel economy may not be great.
Therefore, driving efficiency and drivability of an 8-speed automatic transmission may be deteriorated, and thus, gear ratio span larger than 9.0 is necessary.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.